Wedge-shaped chock means for locking impression blocks of a die assembly

ABSTRACT

An expansion-gap-compensating system for a die that is especially useful in the area of high-temperature diecasting, e.g., at temperatures of about 1,300* F. and up. When a die&#39;&#39;s impression block is fabricated of a metal having a different expansion coefficient than that of the die&#39;&#39;s holding block crevasses or expansion gaps tend to open between the two blocks upon heating of the die assembly to high temperature from room temperature. The width of these expansion gaps is mainly dependent on the difference in expansion coefficients of the block metals and on the casting or operating temperature. The system of this invention permits an impression block and a holding block fabricated of, for example, a refractory metal and a steel respectively, (a) to be simply and easily assembled and maintained together as a die in tight and safe operating relation without damage to either, and (b) to be maintained in an exact centered or preset position relative one to another, at all times throughout a casting run. Thus, the expansion-gap-compensating system acts to compensate for expansion gaps that tend to open between related impression and holding blocks as the die assembly is heated up to and operated at high temperatures, as well as to compensate for the contracting of those gaps as the die assembly cools after the casting run.

United States Patent [72] Inventor Joseph A. Woltering Hamilton, Ohio [21] Appl. No. 19,240

[22] Filed Mar. 13, 1970 [45] Patented Sept. 28, 1971 [73] Assignee Hamilton Die Cast, Inc.

Hamilton, Ohio Continuation of application Ser. No. 737,480, June 17, 1968, now abandoned.

[54] WEDGE-SHAPED CHOCK MEANS FOR LOCKING IMPRESSIONBLOCKS OF A DIE ASSEMBLY 4 Claims, 4 Drawing Figs.

[52] US. Cl. 164/339, 18/42 D, 164/303 [51] lm. (I 822d 17/00 [50] Field of Search 249/82,

160,165, 166; 18/42 R, 44 R, 42 D; 164/342, 303, 341,113, 312, 339

[56] References Cited FOREIGN PATENTS 186,785 11/1955 Austria 164/342 1,316,838 12/1962 France 164/342 Primary ExaminerRobert D. Baldwin Attorney-Wood, Herron & Evans ABSTRACT: An expansion-gap-compensating system for a die that is especially useful in the area of high-temperature diecasting, e.g., at temperatures of about 1,300 F. and up. When a dies impression block is fabricated of a metal having a different expansion coefficient than that of the dies holding block crevasses or expansion gaps tend to open between the two blocks upon heating of the die assembly to high temperature from room temperature. The width of these expansion gaps is mainly dependent on the difference in expansion coefficients of the block metals and on the casting or operating temperature. The system of this invention permits an impression block and a holding block fabricated of, for example, a refractory metal and a steel respectively, (a) to be simply and easily assembled and maintained together as a die in tight and safe operating relation without damage to either, and (b) to be maintained in an exact centered or preset position relative one to another, at all times throughout a casting run. Thus, the expansion-gap-compensating system acts to compensate for expansion gaps that tend to open between related impression and holding blocks as the die assembly is heated up to and operated at high temperatures, as well as to compensate for the contracting of those gaps as the die assembly cools after the casting run.

PA mEn'ssrzm V TE W W 2 3,608,623

:IITM/VIXI WEDGE-SHAPED CHOCK MEANS FOR LOCKING IMPRILSSION BLOCKS OF A DIE ASSEMBLY This application is a continuation application of U.S. Ser. No. 737,480, filed June 17, 1968, now abandoned. This invention relates to dies and, more particularly, relates to an expansion-gap-compensating system that is especially advantageous for dies used when casting high melting point materials.

Die casting is a well-known method of forming cast metal parts; it basically involves injecting a molten metal charge under pressure into a die cavity. The basic components of a diecasting-type machine are a die assembly of two halves or dies that together define a negative impression or cavity of the object that is desired, a chamber for holding a charge of mo]- ten metal, and a plunger for transferring the metal charge under pressure from the chamber to the die. The basic functions of such a machine are to close and hold the two halves or dies of the die assembly tightly together for establishing the die cavity; to inject the molten metal under pressure into the die cavity; and then to open the die assembly and eject the finished casting from the cavity.

The die assembly for diecasting-type machines basically consists of two separate halves or dies, each containing a part of the casting impression, plus cores if needed for the part to be casted. The die halves are mounted on the diecasting machine and are so arranged that one is stationary (called the cover die) while the other is movable (called the ejector die). The mating surface or front face of each die is finished so that the dies fit snugly together at an interface to form the die cavity when in the closed position. When the machine is closed the two halves of the die assembly are locked tightly together in precise register, after which the molten metal is injected from the injection apparatus under pressure into the die cavity so formed through a gate in the assembly. Subsequently, the two die halves are drawn apart to allow ejection of the casting. Proper means for rapidly ejecting the casting from the die assembly is provided in the form of ejector pins mounted to an ejector plate reciprocably assembled with the ejector die. Thus, the movable or ejector die usually contains, in addition to a portion of the casting impression, movable elements such as cores, slides, and ejector mechanism.

The material from which the die cavity is formed is one factor in determining the commercial success of the diecasting process. Dies are, of necessity, expensive and the money expended in fabricating them must be justified-by good service life as measured by number of castings produced. Since the molten metal is forced into the die cavity under pressure the die must be capable of withstanding impact and mechanical shock, and because the metal is molten and at a relatively high temperature the die must be capable of withstanding thermal shock as well. Also, and very importantly, the die must be able to resist washing or erosion of the cavity configuration by the metal being cast. The combination of these three factors, plus others, means that the die cavity must be constructed of very good quality steels. With the lower melting point alloys used in diecasting, for example, tin, lead, and zinc, the problem of securing a long life for the die at an economical per casting cost is not so acute. However, with the higher melting point alloys, for example, magnesium, aluminum, gray iron, and copper-zinc alloys, the die steel must be of the best possible grade tool steel and must be produced to quite rigid specifications to overcome, in particular, the cavity erosion or wash problem.

With the casting of such high melting point metals as are presently used in the die casting industry, for example, the magnesium, aluminum, gray iron, and copper-zinc alloys, and with diecasting technology rapidly approaching that point where even higher melting point metals will be diecast, the problems of eroding and washing of the die cavity configuration and thermal shock to the die are particularly acute because of those metals high melting points. In an effort to combat this problem there has been developed a structural die design which comprises a separate impression block for each of the ejector and cover die halves. The impression blocks together define the casting configuration, each impression block being carried in a pocket or nest defined by its associated holding block. Thus, the ejector die half and the cover die half is each comprised of an impression block and a holding block mated or nested together. To hold the two blocks of each die together the impression block is usually friction fit into the pocket of its related holding block, i.e., the outer periphery of the impression block is substantially equal to the periphery of the holding blocks pocket. In general practice, both blocks have been formed from steel. The system of providing an impression block-holding block structure for a die half admits of substantial economy because only the impression block need be replaced, and not the entire die, when the cavity configuration becomes so eroded or washed out that an undesirable percentage of castings being produced is out of tolerance limits.

it has been found that the present steels known from which dies for diecasting-type machines can be made do not themselves have a high enough melting point, not are they sufficiently rugged, to withstand the eroding and washing characteristic and thermal and mechanical shock characteristics of the high melting point alloys so as to yield a desirable economic production life. To solve this problem it has been proposed to provide impression blocks of refractory metals because that group of metals is relatively resistant to thermal shock and cavity erosion at high diecasting temperatures. In the interest of economy, the holding blocks are still fabricated from high quality steels because of the high refractory metal cost. However, refractory metals are particularly brittle at room temperature. Because the only known practical method of maintaining the impression block and holding block in operable engagement is by friction fit techniques, it will be seen that breakage of such impression blocks during the engaging and disengaging of those blocks with their related holding block pockets is a definite problem and economic hazard. Also, when the outer periphery of a refractory metal impression block is configured to conform to the steel holding block pocket in a friction fit relationship at, for example, room temperature, once the die assembly has risen to its operating temperature distinct expansion gaps or crevasses may occur between the periphery of the refractory metal impression block and the periphery of the pocket in its associated steel holding block. This for the reason that the expansion coefficients of the normal steels from which holding blocks are usually fabricated are substantially greater, for example, up to three or four times greater, than the expansion coefficients of the refractory metals from which the impression blocks are fabricated. Such expansion crevasses or clearances or gaps created between the impression block and associated holding block at high die operating temperatures may cause alignment or registry difficulties for the cover and ejector impression blocks during repeated openings and closings of the die halves because of slippage or movement of one or both impression blocks within their holding block pockets, thereby rendering out of tolerance a substantial percentage of the castings produced by the die assembly. The expansion gaps created between the impression block and the holding block of the ejector die half at high die temperatures may even be great enough so that the ejector impression block will actually be ejected from the ejector holding block by the ejector pins, after the die halves have been opened, during ejection of the formed casting. Also, during a production run the molten metal to be cast may squirt out between the interface of the cover and ejector impression blocks and run into and solidify in the expansion crevasses or gaps created, thereby preventing the impression blocks from being removed from the holding block pockets other than by breaking or otherwise cutting out the impression block.

Accordingly, it has been one objective of this invention to provide an expansion-gap-compensating system associated with the impression block and holding block of a die, that is, a die half, that adequately retains and prevents movement of the impression block in the holding block pocket when the expansion coefficient of the impression block material is substantially different from the expansion coefficient of the holding block material.

It has been another objective of this invention to provide an expansion-gap-compensating system for a die's impression and holding blocks, when those blocks are made of materials having difi'erent expansion coefiicients, that is easily and readily adjustable during a casting run whereby, as the die assembly rises to operating temperature from room temperature upon startup, as well as during the casting run, the system may be periodically adjusted by an operator as required to compensate for expansion gaps or crevasses that may tend to open, i.e., to compensate for the differential material expansion, and as the die assembly declines from operating temperature the system may be periodically adjusted as required to compensate for the contracting of those expansion gaps, i.e., to compensate for the differential material contraction.

It has been a further objective of this invention to provide an expansion gap system for a dies impression and holding blocks, when those blocks are made of materials having different expansion coefficients, that precludes movement of each impression block relative to its associated holding block even during repeated adjustments of the system by an operator so as to permit opposed impression blocks of a die assembly to be maintained in proper registry throughout a casting run.

These objectives have been attained in this invention by providing an expansion-gap-compensating system for a die comprising, in combination and in preferred embodiment form, (a) a holding block (fabricated of, for example, a steel) with a pocket defined therein, (b) an impression block (fabricated of, for example, a refractory metal) receivable within the pocket, the impression block having a substantially shorter peripheral length than the pocket so that when the two blocks are assembled a continuous fixed gap equal in length to at least one-half the peripheral length of the impression block is created between the impression block and the holding block, (c) a chock positionable in wedging fashion within the fixed gap for maintaining the blocks together as a die, and (d) a key engageable with keyways in the bottom of the pocket and the impression block for establishing and maintaining accurate relative position of the blocks one to the other. Each chock is provided with adjustment means so that it can be tightened or loosened within the fixed gap depending on the relative expansion or contraction of the blocks and the crevasses or expansion gaps between the blocks that tend to be formed thereby. The expansion-gap-compensating system of this invention permits the impression block and the holding block of a die, each of which is fabricated of a material having a different expansion coefficient from the other, to be simply and easily assembled and maintained together as a die in tight and safe operating relation without damage to either, and to be maintained in an exact centered or preset position relative one to the other even during repeated adjustments of the system by an operator, at all times throughout a casting run.

Other objectives and advantages of this invention will be more apparent from the following detailed description taken in conjunction with the drawings in which:

FIG. 1 is an axial cross-sectional view of a die assembly incorporating the expansion-gap-compensating system of this invention;

FIG. 2 is an elevational view, partially in cross section, taken along lines 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along lines 33 of FIG. 2; and

FIG. 4 is a cross-sectional view of an alternate impression block embodiment useful with the expansion-gap-compensating system.

As illustrated in FIGS. 1-3, the principles of this invention are incorporated in a die assembly having an ejector or movable die and a cover or fixed die 11, the die halves being held in operational engagement one with the other so as to define a die cavity 12 by apparatus, not shown, associated with any known type of diecasting machine. The ejector die 10 is comprised of an ejector shoe or holding block 13 (fabricated of, for example, a tool steel) which establishes a rectangular nest or pocket 14 in the front face of block 13. The pocket 14 is sized to receive an ejector impression block 15 and an ejector gate block 16 (both fabricated of, for example, a refractory metal) from the front face of holding block 13, and is defined by vertical sidewalls l7 and a flat bottom 18 parallel to the front face of the holding block 13. The bottom 18 of the pocket 14 provided structural support for the impression block 15 when a charge of molten metal is received in the die cavity 12.

The impression block 15 and the gate block 16 are abutted end-to-end at joint 19 in the pocket 14, and the free end of the gate block abuts gate end 21 of the pocket. It will be noted that the overall length L of the abutted impression block 15- gate block 16 combination is substantially less than the length L of the pocket 14 so as to create an end gap 23 at one end between the impression block and the pocket end 22, see FIG. 2. Also, it will be noted that the widths W of the impression block 15 and gate block 16 are substantially less than the width W of the holding blocks pocket 14 so as to create side gaps 24, 25 on both sides between the sides of the impressionblock-15/gate-block-16 combination and the related pocket sides 17, see FIG. 2. Thus, the abutted impression-block- 15/gate-block-16 combination has a shorter outer peripheral length than the peripheral length of the pocket 14, thereby creating the fixed gaps 23-25 that establish a single, continuous, fixed gap between the impression-block/gate-block sides and three sides 17, 17 and 22 of the pocket s four sides when those blocks are assembled together. It is to be noted that the continuous fixed gap 23-25 is preferably equal in length to at least one-half the peripheral length of the impression-blockl5/gate-block-l6 structure and, in the figures, is shown as being almost percent the peripheral length of the gateblock/impression-block structure.

The ejector gate block 16 can move from one side to the other between sides 17 of the pocket 14 because very precise positioning of this block 16 within the pocket is not required, that is, if the gate block is off center by some hundredths of an inch this will not ordinarily adversely affect the quality of the castings produced. The ejector impression block 15, however, is positioned within the pocket 14 by a rectangular key 27 extending lengthwise of the pocket, see FIG. 1. The key 27 is received in mating keyways 28, 29 sized to fit key 27, the keyways being cut into the bottom 18 of the pocket 14 and into the bottom of the impression block 15 respectively. The key 27 is fixed to holding block 13 in keyway 24 by two bolts 31 the heads of which are recessed in the key. The key 27 serves to maintain the impression block 15 in a precise, preset position within the pocket 14 at all times, thereby preventing movement of the impression block within the pocket relative to the holding block 13 in both the north-south and east-west directions even when expansion gaps tend to open between the two blocks during use.

The ejector die 10 is also illustrated as having two ejector pins 26 that are selectively reciprocable into the die cavity 12 by ejector apparatus, not shown, so as to eject castings formed in the cavity when the dies 10, 11 are opened.

In describing the cover die 11, elements of the cover die structure that are similar to like parts of the ejector die 10 structure are given the same reference number as used in describing the ejector die except that the letter a follows that number. The cover die 11 includes a cover holding block 13a that defines a cover nest or pocket 14a in the front face of block 13a, the pocket 14a and block 13a having substantially the same peripheral dimensions and geometry as pocket 14 and ejector holding block 13. An impression block 15a and gate block 16a are abutted end to end at joint 19a in the pocket 14a in mirror relation to the impression block 15 and gate block 16 of the ejector die 10, see FIG. 1. The cover impression 15a and gate 16a blocks are of substantially the same outer peripheral dimensions and outer geometry as the ejector impression 15 and gate 16 blocks. Thus, fixed gaps 23a25a substantially equal in dimension and configuration to fixed gaps 23-25 of the ejector die are also established for the cover die 11 between sides l7a-17a and ends 21a, 22a of the cover block's pocket 14a and the sides of the impressionblock-l5a/gate-block-l6a combination. The cover gate block 160 and holding block 1311 are dissimilar from the ejector gate 16 and holding blocks 13 in that they cooperate to define a gate or molten metal inlet 33 for the die cavity 12. The inlet 33 receives the end 34 of a shot tube 35 passing through passageway 36 in the holding block 130 and gate block 16a. A flange 37 integral with the shot tube 35 is seated on the back of the holding block 13a to position the shot tube relative to the gate 33. The shot tube 35 is part of a diecasting machine, not completely shown.

The shot tube 35, being fixed, serves to maintain the gate block 16a in its preset position within pocket 14a. As with the ejector die 10, the cover impression block 15a is positioned within the pocket 144 by means of a rectangular key 27a located in keyways 28a, 29a cut in the bottom 13a of the pocket 14a and the bottom of the impression block 15a, respectively. The key 27a is fixed to holding block 13a in keyway 23a by bolts 32a in the same manner as for the ejector die 10.

As can be seen from the figures, when the two dies 10, 11 are closed into cavity 12 forming relation for receiving a charge of molten metal they meet at their front faces, that is, at die interface 41. The impression blocks 15, 15a cooperate to form the die cavity 12 which, in the figures, is illustrated as that of a standard test bar. The gate blocks 16, 16a cooperate to establish the gate or metal inlet 33 for the molten metal, the gate terminating in an end feeder area 42 that distributes the molten metal into the die cavity 12. Guide pins 33 are mounted to the cover holding block 13a and are receivable in recesses 39 formed in the ejector holding block 13 for centering or locating the holding blocks 13, 13a in register when they are closed into operable die casting position. When the dies 10, l 1 are opened to eject a casting and then again closed to form cavity 12, keys 27, 27a act to ensure that impression block 15, 15a will be in registry by maintaining the preset position of the impression blocks relative to their holding blocks 13, 13a even if expansion gaps or crevasses occur between the two blocks during the casting operation. Movement of the ejector impression block 15 relative to the cover impression block 150 only a few thousandths of an inch may, in complex casting configurations, so misalign those blocks 15, 15a when they are closed together that castings produced from them will be out of dimensional tolerance limits. Thus, keys 27, 27a play an important part in maintaining the position of impression blocks 15, 150 within their pockets 14, 14a and, in combination with guide pins 38 and recesses 39, maintain the registry of the impression blocks during repeated openings and closings of the die assembly even when expansion gaps between impression and holding blocks occur.

Each impression-block-l5,-l5a/gate-block-16,-16a combination in each holding block's pocket 14, 14a, respectively, is maintained in that pocket during use of the die assembly by restraining means or chocks 43, 43a engageable with each die 110), 11 from the front face of that die. The chocks 43, 430 are preferably trapezoidal or wedge-shaped in cross-sectional configuration, each chock having parallel top 44, 44a and bottom 45, 45a sides, a tapered side 46, 46a and a vertical side 47, 47a, the inwardly tapered sides meeting the top sides at an acute angle a, see FIG. 3.

The chocks 43, 430 are positioned within and sized to fit in the fixed gaps 23-25, 230-250 created when the impression 115, 15a, gate 16, 16a, and holding 13, 13a blocks are assembled to substantially frame each block 15, 16 and 15a, 16a unit in its related pocket 14, 14a, see FIGS. 1 and 3.

The impression blocks 15, 15:: are provided with outwardly tapered sides 48, 48a in an obtuse angle B, see FIG. 3. The sum of the angles a and [3 equals 180. Thus, the inwardly tapered sides 46, 46a of the chocks 43, 43a are angled to cooperate with outwardly tapered sides 48, 43a of the impression 15, E511 and gate 116, Ma blocks so as to restrain those blocks in their respective pockets 14, 14a. In essence, each impression-block/gate-block unit is restrained and, thereby, retained, in its pocket because of the wedging action of the chocks between the impression 15, 15a and gate 16, lion blocks and the holding blocks 13, 113a.

it is to be noted that the chocks 43, 43a are of a thickness T substantially less than the depth D of the pockets H4, 1140 so they can be adjusted downward if required, as is more fully explained hereinafter. The top side 44, width of each chock 43, 43a is preferably about equal to or a little less than the width at interface 41 of the fixed gaps 23-25, 2311-2511 that the chock is to serve when the die is at room temperature. Thus, when the chocks 43, 43a are initially positioned in a room temperature holding block 113, 13a during makeup of the die the top sides 44, 44a of the chocks are substantially parallel with the front faces of the die halves 10, 11, see FIG. 3, and substantial clearance 49, 49a is established between the bottom side 45, a of the chocks and the bottom 18, 18a of the pockets 11-4, 14a.

The chocks 43, 43a are maintained in operating position, and are adjustably positionable within fixed gaps 23-25, 2311-25 during heatup, operatiomand cooldown of the die, by adjustment means in the form of threaded bolts 50, 50a spaced along their length in mirror relation for the ejector die 10 and the cover die 11; the bolts are available to an operator for adjustment from the front face of each die. The bolts 50, 500 are engageable with the holding blocks 13, 13a by threads 52, 52a that pass through, without threadedly engaging, the chocks 43, 43a. Each bolthead 54, 54a cooperates with a recessed shoulder 53, 53a in each chock 43, 43a for forcing the chock down toward the bottom of its related pocket 14, 14a when the bolts 50, 500 are tightened into the holding blocks 13, 13a. Thus, by virtue of the wedging action performed by the chocks 43, 43a in the fixed gaps 23-25, 23a-25 between the tapered sides of the impression-gate block units and the sides 17, 17a, 22, 22a of the holding block pockets l4, 14a (the pressure of which can be varied or ad- 40 justed by bolts 50, 53a) the impression blocks 15, 15a and gate blocks 116, 16a are easily and simply assembled and, thereafter, may be maintained together in tight and safe assembly during casting operations even when expansion gaps tend to occur due to difierent block material expansion coefficients and high temperatures.

As is illustrated in FIGS. 1 and 3, the chock 43, 43a structure is substantially the same for the chocks used with both the ejector die lit) and the cover die 11, except that the depth of the working shoulder 53 from the chocks top side 44 for the ejector die chocks 43 is substantially deeper than that depth for the cover die chocks 43a. It is preferred that shoulders 53a of the chocks 43a be recessed to a depth substantially less than the height of the boltheads 53a, and it is preferred that the shoulders 53 of the chocks 43 be of substantially greater depth than the height of the boltheads 54. This for the reason that when the ejector it) and cover 11 dies are mated in operating relation, and because of the symmetry and mirror relation of the die assembly, the heads 54a of the cover chock bolts 5011 will be partially received within the deeper recesses of chock 43 where the bolts 50 are positioned, see FIGS. 1 and 3. Such a relationship prevents molten metal from being forced into the area 55 between heads 54, 54a of the adjusting bolts during a casting cycle. If metal got into this area 55 it could fuse the boltheads 54, 54a together and hinder separation of the die halves W, M. if, for example, Allen head bolts are used and metal fills the wrench recess on the Allen head, removal of the adjusting bolts 50, 500 from the chocks 43, 43a and holding blocks 13, 13a also would be extremely difficult.

The chock 43, 43a structure of this invention admits of a method of use which is unique and novel in that it easily and simply permits the impression block 115, 15a to be changed with its related holding block 13, 1311. That is, the necessity for a tight friction fit between the impression block 15, 15a and holding block 13, 13a has been eliminated by the method and structure of this invention, thereby lessening the practical problems that obtain when handling, for example, refractory metal impression blocks which are relatively brittle at room temperature. In use, the impression block 15, a and gate block 16, 160 are placed in the holding block's pocket 14, 14a from the front face of the die 10, 11, those blocks and pocket being formed so as to create fixed gaps 23-25, 23a-25a between the sides of the impression blocks 15, 15a and the sides 17, 17a, 22, 22a of the holding block pocket 14, 14a. The key 27, 27a is positioned in the keyways 28-29, 28a-29a provided in the bottom 18, 18a of the pocket 14, 14a and the bottom of the impression block 15, 15a, thereby centering the impression block in the holding blocks pocket. Because the impression-block/gate-block unit is formed with a peripheral length less than the peripheral length of the holding blocks pocket 14, 14a the impression block 15, 15a can be easily and gently set down into the holding blocks pocket. This is of substantial advantage for refractory metal impression blocks in that it lessens the chance of cracking through mishandling. Subsequently, the chocks 43, 43a are positioned within those gaps 23-25, 23a-25a from the front face of the die 10, 11 in a wedging fashion so as to maintain the impression block 15, 15a immobile relative to the holding block 13, 13a. The chocks 43, 430 are tightened in position from the front face of the die 10, l 1 by tightening the bolts 50, 50a and, thus, the impression block 15, 15a is tightly and safely restrained in operating assembly with the holding block 13, 13a. Even if the chocks 43, 430 are tightened with unequal pressure on either side of the impression block 15, 15a, those blocks still maintain their preselected alignment because of the key 27, 27a and keyways 28-29, 28a-29a. Such a method and structure has been found to substantially reduce the amount of time required by an operator to change impression blocks in a holding block.

The problems that occur when using a refractory metal impression block 15, 150 with a normal grade steel holding block 13, 13a arise because of the difference in expansion coefficients between these materials, as heretofore explained. The refractory metals have a much lower coefficient of expansion than do steels, for example, a refractory metal alloy may have a coefficient of expansion only one-half to one-third that of a good grade steel. Hence, in the prior art, even though an impression block may have a tight friction fit with the holding block's pocket when it is first assembled in operating position with that pocket at room temperature, as the die assembly heats up to operating temperature the sides of the pocket of the steel holding block tend to expand away from the sides of the refractory metal impression block. That is, the impression block does not expand as much as the holding block to maintain the tight friction fit; therefore, expansion gaps or crevasses are formed during high-temperature operation between the impression block and the sides of the holding blocks pocket when the prior art method of holding the two blocks in operating engagement is used. In solving these problems, the chock 43, 43a structure of this invention is utilized by the method steps of periodically tightening the chocks 43, 43a from the front face of the die 10, 11 as the die heats up to operating temperature by means of adjusting bolts 50, 50a to take up any expansion gaps or crevasses created, thereby maintaining the impression block in tight and safe operating assembly with the holding block 13, 13a. This step drives the wedge-shaped chocks 43, 43a deeper into the fixed gap 23-25, 23a-25a, but the original clearance 49, 49a between the bottom 18, 18a of the pockets 14, 14a and the bottom 45, 45a of the chocks permits such limited movement to be achieved. Such tightening of bolts 50. 50a also can be performed by an operator from the readily accessible front face of each die 10, 11 when the die halves are momentarily parted for ejecting a casting at the end of one casting cycle during a casting run, that is, the die does not have to be dismounted from the casting machine or disassembled to make the required adjustments. After a casting run has been concluded, and as the die assembly is cooling down to room temperature for changing impression blocks 15, 15a (thereby causing the expansion gap formed on heat up to contract), the chocks 43, 43a are periodically loosened by unscrewing bolts 50. This prevents any build up of compressive forces between the holding block 13, 13a and the impression block 15, 15a that may cause the brittle impression block to crack. Thus, this method easily and simply permits takeup of any expansion joint or gap or crevasse created during heatup and operation of the die assembly, thereby maintaining the impression block in tight operating assembly with the holding block during a casting run without the necessity of periodically dismounting or disassembling the die. Also, this method easily and simply permits that gap to be recreated or opened as the die assembly is cooled down and the impression 15, 15a and holding 13, 13a blocks contract back to normal room temperature configuration, thereby preventing cracking of the impression block on cooling that may occur if intolerable pressures are created on the brittle refractory metal impression blocks.

When the impression block 15, 15a is fabricated of, for example, a refractory metal and the holding block 13, 13a is fabricated of, for example, a tool steel it is preferred that the chocks 43, 43:; be fabricated of that tool steel and the key 27 270 be fabricated of that refractory metal. In the case of the chocks 43, 43a, they must usually be made of steel so they can withstand the stresses placed on them by tightening of the bolts 50, 50a. In the case of the key 27, 27a, it is desirably fabricated of the same material as the impression block 15, 15a so that no slippage or gaps occur between the key and its related impression blocks because both expand and contract at equal rates. Even if small gaps occur between the key 27, 27a and the holding block keyway 28, 28a, because the key is bolted to the holding block 13, 13a such gaps cannot adversely affect the centered position of the impression and holding blocks, Thus, in the very important phase of registry or block alignment it is by means of the key 27, 27a, keyways 28-29, 28a-29b, and bolts 31, 31a fixing the keys to the holding blocks 13, 13a that the impression blocks 15, 15a are maintained in a centered position relative to the holding blocks pockets 14, 140. Over tightening on one of the chocks 43, 430 by an operator relative to another of the chocks may inadvertently move the impression block 15, 15a off center a substantial number of thousandths of an inch without the key-keyway structure; however, this structure prevents such a happenstance from occurring.

The impression blocks 15, 15a illustrated in FIGS. l-3 have been shown as defining a single die cavity. However, an alternative embodiment for the impression block, as illustrated in FIG. 4, is one having one-half 61 of a first die cavity on its front face 62 and one-half 63 of a second die cavity on its back face 64. This alternative embodiment can be flipped over in a holding blocks pocket when a casting configuration change is required. Such an impression block die admits of substantial economy particularly when that block is formed of a high cost material such as a refractory metal in that two castings, instead of just one, can be cast from it. As can be seen from FIG. 4, the cross-sectional angle {3 defined by each face 62, 64 with the tapered sides 65 of the impression block is an obtuse angle, thereby making such a block configuration useful with the expansion gap system of this invention.

Although I have described the preferred embodiment of my invention in complete detail it will be understood by those skilled in the art that variations and modifications may be established in the expansion gap system structure and method of this invention as described herein without departing from the spirit or scope of the appended claims. For example, even though the inventive concept of this application has been described primarily with reference to the art of diecasting, it will be understood that the inventive principles are also applicable to permanent molding, centrifugal molding, gravity molding and other related areas where a die is utilized comprised of a holding block and an impression block wherein the expansion coefficients of those block materials cause problem(s) such as are discussed above.

Accordingly, having fully disclosed the preferred embodiment of my invention, what I desire to claim and protect by Letters Patent is:

l. A die assembly particularly adapted for use in the molding or casting of materials comprising, in combination,

a movable die half and a fixed die half each of which include a holding block having a pocket defined in the front face thereof,

an impression block having at least one outwardly tapered side established in nested position within each of said holding blocks pockets, each of said impression blocks having a substantially shorter peripheral length than the pocket in its associated holding block so that a preformed gap is created between the tapered sides of each impression block and its associated holding block at the face of said die half,

at least one chock associated with each pair of said impression and holding blocks, said chocks being wedge-shaped in cross-sectional configuration and being positioned within said prefonned gaps for holding each pair of said impression and holding blocks in fixed and immobile relation relative one to the other,

at least one bolt interconnecting each of said chocks with a holding block for tightening the associated chock, impression and holding blocks into fixed and immobile relation, and

means for charging molding or casting material into the die cavity defined by said impression blocks.

2. A die assembly as set forth in claim 1 wherein said bolts are threadedly connected to said holding blocks and are accessible for adjustment from the faces of said die halves.

3. A die assembly particularly adapted for use in the molding or casting of materials comprising, in combination,

a movable die half and a fixed die half each of which include a holding block having a pocket defined in the front face thereof,

an impression block established in nested position within each of said holding blocks pockets, each of said impression blocks having a substantially shorter peripheral length than the pocket in its associated holding bloclr so that a preformed gap is created between the tapered sides of each impression block and its associated holding block at the face of said die half,

at least one wedge-shaped chock associated with each pair of said impression and holding blocks, said chocks being positioned within said preformed gaps for holding each pair of said impression and holding blocks in fixed and immobile relation relative one to the other, and

at least one bolt passing through each of said chocks into connecting engagement with a holding block for tightening the associated chock, impression and holding blocks into fixed and immobile relation, the head of each bolt bearing against a working shoulder formed in that chock and recessed beneath the top side of that chock such that said bolt can be adjusted from the front face of the die half,

the working shoulder of one of said movable die halfs chock and said fixed die halfs chock being recessed to a depth substantially greater than the height of that bolts head holding that chock in fixed and immobile assembly, and the working shoulder of the other of said movable die halfs chock and said fixed die halfs chock being recessed to a depth substantially less than the height of that bolts head holding that chock in fixed and immobile assembly,

the bolt of said movable die half's chock being positioned in mirror relation to the bolt of said fixed die half's chock such that the shallower recessed bolt head is received in the recess of the deeper recessed bolt head when the fixed and movable die halves are in the closed position that defines the mold cavity, and

means for charging molding or casting material into the die cavi definedb said impression blocks. 4. A re assemby as set forth in claim 3 wherein said preformed gap is equal to at least about one-half the peripheral length of said impression block, wherein at least two chocks are associated with each pair of said impression and holding blocks, and wherein a series of bolts interconnect said chocks and said holding blocks. 

1. A die assembly particularly adapted for use in the molding or casting of materials comprising, in combination, a movable die half and a fixed die half each of which include a holding block having a pocket defined in the front face thereof, an impression block having at least one outwardly tapered side established in nested position within each of said holding blocks'' pockets, each of said impression blocks having a substantially shorter peripheral length than the pocket in its associated holding block so that a preformed gap is created between the tapered sides of each impression block and its associated holding block at the face of said die half, at least one chock associated with each pair of said impression and holding blocks, said chocks being wedge-shaped in crosssectional configuration and being positioned within said preformed gaps for holding each pair of said impression and holding blocks in fixed and immobile relation relative one to the other, at least one bolt interconnecting each of said chocks with a holding block for tightening the associated chock, impression and holding blocks into fixed and immobile relation, and means for charging molding or casting material into the die cavity defined by said impression blocks.
 2. A die assembly as set forth in claim 1 wherein said bolts are threadedly connected to said holding blocks and are accessible for adjustment from the faces of said die halves.
 3. A die assembly particularly adapted for use in the molding or casting of materials comprising, in combination, a movable die half and a fixed die half each of which include a holding block having a pocket defined in the front face thereof, an impression block established in nested position within each of said holding blocks'' pockets, each of said impression blocks having a substantially shorter peripheral length than the pocket in its associated holding block so that a preformed gap is created bEtween the tapered sides of each impression block and its associated holding block at the face of said die half, at least one wedge-shaped chock associated with each pair of said impression and holding blocks, said chocks being positioned within said preformed gaps for holding each pair of said impression and holding blocks in fixed and immobile relation relative one to the other, and at least one bolt passing through each of said chocks into connecting engagement with a holding block for tightening the associated chock, impression and holding blocks into fixed and immobile relation, the head of each bolt bearing against a working shoulder formed in that chock and recessed beneath the top side of that chock such that said bolt can be adjusted from the front face of the die half, the working shoulder of one of said movable die half''s chock and said fixed die half''s chock being recessed to a depth substantially greater than the height of that bolt''s head holding that chock in fixed and immobile assembly, and the working shoulder of the other of said movable die half''s chock and said fixed die half''s chock being recessed to a depth substantially less than the height of that bolt''s head holding that chock in fixed and immobile assembly, the bolt of said movable die half''s chock being positioned in mirror relation to the bolt of said fixed die half''s chock such that the shallower recessed bolt head is received in the recess of the deeper recessed bolt head when the fixed and movable die halves are in the closed position that defines the mold cavity, and means for charging molding or casting material into the die cavity defined by said impression blocks.
 4. A die assembly as set forth in claim 3 wherein said preformed gap is equal to at least about one-half the peripheral length of said impression block, wherein at least two chocks are associated with each pair of said impression and holding blocks, and wherein a series of bolts interconnect said chocks and said holding blocks. 